Prior art has previously demonstrated that reaction of substrate compounds using elemental fluorine is a highly exothermic process, making it difficult to obtain good yields of the desired products of the reaction and scale-up to industrial production. Attempts to control the reaction have involved the use of the dilute fluorine (1-20%) in an inert diluent (N.sub.2, He, Ar) at low temperature (-70.degree. C. to -85.degree. C.) and use of an inert solvent (CFCl.sub.3, CF.sub.2 Cl.sub.2, CFCl.sub.2 CF.sub.2 Cl) [Eur. Pat. Appl. No. 0 219 823 Al dated Apr. 29, 1987; S. Rozen and C. Gal, J. Org. Chem, (1987), 52 2769]. European Patent Application No. 0,219,823 teaches dilution of fluorine with an inert gas wherein the molar ratio of inert gas to F.sub.2 is from 5:1 to 15:1. Even with the use of such mild conditions, in order to control the exotherm and prevent unwanted side reactions, the rate of fluorine addition is less than 80 ml min.sup.1 (less than 7.6g hr.sup.-1), thus making large scale reactions impractical. Other techniques, such as the "LaMar" method [for example R. J. Lagow et al, J. Org. Chem, (1989), 54 1990] or Aersol Direct Fluorination [J.L. Adcock et al, J. Am. Chem Soc., (1981), 103 6937] both involve sophisticated apparatus and low F.sub.2 flow rates (less than 60 ml min.sup.-1), again unsuitable for large-scale production. It has now been discovered that by the use of an eductor for the introduction of fluorine, preferably in a loop reactor having cooling zones, e.g., cooling coils equipped to be externally cooled, substrate compounds can be treated with fluorine rapidly in a controlled manner with fluorine rates as high as possible based on desired reaction control, thus making large-scale fluorine reaction a viable process. Substrate compounds that can be treated with fluorine by this process include, but are not limited to alkenes, cycloalkenes, alkynes, allenes, aliphatics, cycloaliphatics, aromatics, compounds with multiple bonds ##STR1## etc.,) compounds of sulfur, nitrogen, phosphorus, iodine, bromine, chlorine, oxygen, silicon, and the like. Such compounds can be organic or inorganic. The term "fluorination" is used herein in its broadest sense: fluorine can react by addition, substitution, oxidation, polymerization and any other reaction where fluorine may, or may not, be present in the final product. Thus there is used the term "substrate compound" to contemplate as a starting material any compound having fluorine-reactive sites.